The utility of liquid stabilizers is well recognized throughout the plastics industry and liquid stabilizer systems suitable for use with PVC and other resins have been disclosed. The principal advantage of liquid stabilizer systems is the ease of handling and the ability to rapidly and uniformly disperse the stabilizer in the resin so that optimum stabilization can be quickly and consistently achieved.
In U.S. Pat. No. 3,759,856 we have disclosed liquid stabilizers obtained by mixing the Group II metal halide with a polyglycerol partial ester and the use of these stabilizer compositions with vinyl halide resins to impart improved antistatic and antifogging properties in addition to stabilizing the resin against the deleterious affects of oxygen, heat and light. While the metal halide/polyglycerol partial ester stabilizers impart excellent thermal stability to PVC it has been found that the resins show some yellowing after only about ten minutes processing. While the resins do not appreciably discolor until very near the point of thermal degradation the early color formation is nevertheless undesirable to the plastic processor since it makes it difficult to match the colors of different batches, prevents the use of the resin for applications where water-white formulations are required and makes it difficult to work off regrinds of trimmings and other waste materials. It would be highly desirable and advantageous if highly compatible liquid stabilizers resistant to early color formation were available.